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1 University of Wyoming, Laramie, Wyoming, United States
2 Saint Louis University, St. Louis, Missouri, United States
* To whom correspondence should be addressed. E-mail: jren{at}uwyo.edu.
Intermedin (IMD), also called adrenomedullin-2, is a 47-amino acid peptide from the calcitonin-gene related peptide (CGRP)/adrenomedullin family of peptides. Recent studies suggest that IMD may participate in the regulation of cardiovascular function, fluid and electrolyte homeostasis. To evaluate the role of IMD on cardiomyocyte contractile function, electrically paced murine ventricular myocytes were acutely exposed to IMD and the following indices were determined: peak shortening (PS), time-to-PS (TPS), time-to-90% relengthening (TR90) and maximal velocity of shortening and relengthening (± dL/dt). Intracellular Ca2+ was assessed using fura-2AM fluorescent microscopy. Our results revealed that IMD (10 pM - 10nM) significantly increased PS and ± dL/dt in ventricular myocytes, the maximal effect of which (~46%) was somewhat comparable to those elicited by CGRP (1 nM) and adrenomedullin (100 nM). Exposure of IMD significantly shortened TR90 without affecting TPS, similar to CGRP and adrenomedullin. IMD also enhanced intracellular Ca2+ release with a maximal increase of ~50%, and facilitated the intracellular Ca2+ decay rate. The IMD-induced effects were abolished by the protein kinase C (PKC) inhibitor chelerythrine (1 µM), downregulation of PKC using phorbol 12-myristate 13-acetate (1 µM) and the protein kinase A (PKA) inhibitor H89 (1 µM). Our data suggests IMD acutely augments cardiomyocyte contractile function through, at least in part, a PKC and PKA-dependent mechanism.
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